Automatic measurement of electron-beam diameter and astigmatism: BEAMETR

Abstract

Abstract Beam size is one of the major characteristics of any electron beam system. Accuracy and resolution of SEM and an EBL system directly depend on beam diameter; it should be monitored and tuned frequently. Currently used methods are not accurate and are operator dependent. A technique is described to determine beam size using an automatic procedure. In the developed method, a specially designed and fabricated test pattern is scanned using an e-beam. A spectra of the signal is analyzed; beam diameter i s automatically determined using a software program. Results of design, fabrication, and analysis of the beam calibration test pattern are presented. © 2008 Elsevier B.V. All rights reserved. PACS: 07.05.Hd; 68.37.Hk Keywords: Electron probe diameter; Software; SEM resolution 1. Introduction The performance of electron-beam lithography (EBL) systems and scanning electron microscopes (SEM) greatly depends on the beam diameter, astigmatism, and the current distribution within the bea m. Consequently, beam size should be monitored and tuned frequently, but the most widely used technique to m easure beam size, edge detection, is not accurate, and more than it is operator dependent. In this method, a beam is scanned across a sharp edge; the resulting SEM signal is differentiated (see Fig. 1a) and this profile is then wide ly believed to represen t the shape of the beam. However, the edge technique involves two major errors: (a) It is a subject to an areaŽ error due to variable region cut by the edge which produce the SEM signal. As a result, for non-rectangular beams, the width of the differentiated SEM signal is smaller than the actual beam size, see Fig. 1b.